1. Field of the Invention
The present invention relates to a method and system for reducing noise in signal systems. More specifically, the present invention relates to a method and system for reducing noise in information processing systems including audio and graphic image display systems.
2. Description of the Related Art
The recent surge in popularity and low cost for digital photography has advanced signal processing technology such that these devices increasingly provide cleaner sound and clearer picture. Also, increasingly digital images are transmitted among consumers, for example, over the internet using email programs and the like, because they find it more convenient than conventional time consuming film developing processes.
Most digital image processing systems include an image sensor such as a Complementary Metal Oxide Semiconductor (CMOS) or a Charge Coupled Device (CCD) detector. However, in handheld devices such as mobile telephones and personal digital assistants, for example, due to size constraints, the lenses used for the CMOS or CCD cameras have a very limited light collection area. Additionally, although CMOS sensors are preferred over CCD sensors in many applications and devices due to cost considerations, CMOS sensors have a much higher readout noise, thus rendering the overall image noisy.
In operation, a typical image sensor detects light by converting impinging photons into electrons and collecting (integrating) them in sensor pixels. After the integration cycle is completed, the electron charge is converted into a voltage that is supplied to the output terminals of the sensor. Typical sources of noise for a sensor, include sensor noise, which is a component of the readout noise created by both the sensor and the electronics themselves, and photon noise which results from the inherent inaccuracy in the measurement of the captured photons. The total noise is approximately equal to the square root of the sum of the square of the readout noise and the square of the photon noise, as illustrated below by equation (1):Total Noise=˜√((readout noise)2+(photon noise)2)  (1)where the photon noise may be determined by the square root of the number of photons.
In the case of images, various noise sources combine to give a total readout noise for the system. For example, the charge output from a sensor representing a particular pixel may not always be the same given the same light accumulation. The sensor noise is typically specified in the performance sheets for a sensor as readout noise. There may also be other noise associated with the signal amplification stage and the analog to digital conversion process which may vary widely depending on the quality of the components used and the circuit design. For example, if the total readout noise is 1% of the full signal detected, it will not be possible to measure an image feature with a certainty better than 1 part in 100 regardless of the dynamic range of the sensor or the bit depth of the digitizer.
Similarly, in the case of audio data, there are also various sources of noise that reduce the quality of the signal. Such noises may be caused, for example, by manufacturing characteristics of the signal detector and other system components, background noise, and processes associated with signal processing such as amplification, filtering, and the like.
The noise estimate for a given signal, either audio or image, may be determined based upon the characteristics of a signal detector, such as the sensor in the case of image data. However, sensors and signal detectors typically detect the noise in addition to the actual signal. Thus, it is desirable to reduce the noise in audio and image signals detected by signal processing systems such that the captured signal information may be displayed or heard with improved quality.